1.  Standard implementations of Win98 have no file
REBOOT.EXE
2.  Standard implementations of  Win98 should put no
EXEcutable files in C:\WINDOWS\Start Menu\Programs\StartUp\
(only LNK files i.e. links to EXEs stored elsewhere.)
3.  It looks as if a virus wrote into your startup routines a
call to this bogus REBOOT.EXE and if the file is not on
your hard drive it looks as if your AV programme deleted
it correctly -- but left behind the bogus file call (because
your PC boots OK.)

Using Windows Explorer navigate to the startup folder:  C:\WINDOWS\Start
Menu\Programs\StartUp\ and remove the shortcut to reboot.exe or if
reboot.exe is actually in the startup folder move it to another
location, Temp for example.  Reboot.exe is not a Microsoft file.  It
could be a valid file from tools/utilities developers but could also be
associated with malware.  Do a search on it on the internet and you will
find more information.  You might want to do a spyware and virus scan on
your machine.

John

I ran a complete virus scan (AVG) and this fixed the problem. Seem that it
was related to my Ad-Aware SE program??